Vacuum-tube repeater circuits



H. 8. HEAD.

VACUUM TUBE REPEATER CIRCUITS.

APPLICATION FILED JULY II, 1919.

1,403,566. Patented Jan. 17, 1922.

//7I e/77"0/'.' Harry 5. Rena HARRY S. READ, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC PATENT OFFICE.

COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

VACUUM-TUBE REPEATER CIRCUITS.

Specification of Letters Patent. Patented Jan, 1'7, 192% Application filed July 11, 1919. Serial No. 310,093.

T 0 all '10 710m it may concern.

Be it known that I, HARRY S. READ, a citizen of the United States, residing at East Orange. in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Vacuum ube Repeater Circuits, of which the following is a full, clear, concise, and exact description.

This invention relates to vacuum tube repeater circuits and more particularly it relates to a multi-stage vacuum tube amplifier set.

As is well known in the art, weak currents or signals may be amplified to any desired degree by impressing them on a plurality of vacuum tube amplifiers arranged to work into each other by suitable circuit connections. In the operation of such a multistage amplifier set it is important that the source of voltage for the output circuit of the tubes be kept substantially constant. Especially is this true of the source of voltage for the output circuit of the first stage or the first few stages of the amplifier set, since any fluctuation of the source of voltage for the first tube would be amplified by the succeeding tubes along with the signal variations and would produce serious distortion in the signals, thereby preventing a faithful copy of the signals from being impressed on the receiving apparatus.

In accordance with this invention, these undesirable fluctuations in the source of voltage for a stage of a vacuum tube set are substantially prevented by the insertion in the output circuit of the amplifier of a second vacuum tube of the three electrode type in such a manner that any variation in the source of voltage will be counterbalanced by a corresponding variation in the internal impedance of the second tube. In the preferred circuit arrangement this is accomplished by utilizing the property of a vacuum tube that within certain limits a change in the potential of the control electrode will produce a much more than proportional change in the space current of the tube. Accordingly, the cathode and anode of the vacuum tube regulator may be connected in series with the source of voltage to be regulated. while the control electrode of the regulator is connected to its cathode through an impedance, preferably a resistance, which is common to the output circuit of the amplifier supplied with current from said source of voltage. The potential of the control electrode of the vacuum tube regulator is therefore determined by the IR drop in this resistance so that any variation in the output current of the amplifier due, for example, to a change in the source of voltage, will change the potential of the control electrode thereby changing the internal impedance of the regulator a much more than proportional amount so as to restrict the change in output current to a small value.

This insertion of a vacuum tube in the output circuit of an amplifier will also prevent the space current of the amplifier from varying in accordance with the incoming signals so that the amplified signals impressed on the next stage of the amplifier set will consist only of variations in volt' age. a feature which is frequently of considerable importance.

This invention will be better understood by reference to the following detailed description taken in connection with the drawing which represents the preferred arrangement of this invention.

Referring to the drawing. 2 and 3 are vacuum tube amplifiers connected in tandem and containing respectively cathodes 4 and 5, anodes 6 and 7 and control electrodes 8 and 9 respectively. Cathodes 4 and 5 are heated by current from a source of voltage 11. Output current for the two amplifiers is supplied by the source of voltage 13. plified, shown in the drawing as a telephone transmitter which is connected to the input circuit of amplifier 2 by an input transformer 15. In the output circuit of tube 3 is shown a suitable receiving apparatus such as a telephone receiver 16 for receiving the signaling impulses from transmitter 14 which have been successively amplified by tubes 2 and 3.

If desired, the secondary of the transformer 15 may be shunted by a high resistance 17 and a source of voltage 18 may be placed in the input circuit of tube 2 to determine .the static potential of grid 8. The output circuit of tube 2 may be traced as follows: Anode 6, resistance 19, cathode 20 and anode 21 of a vacuum tube regulator 22, source of voltage 13 to cathode 4. Control electrode 25 of the vacuum tube regulator is connected through an adjustable source of voltage 26 to that terminal of re 14 is a source of signals to be am- 'the greater this impedance will. be.

sistance 19 which is electrically remote from cathode 20. Thus it is seen that the space current of amplifier 2 depends upon the valueof resistance 19 and the effective impedance between the cathode 20 and anode 21 of the vacuum tube regulator. As is well known in the art, the efiective impedance between these electrodes of the regulator 22 depends upon the potential of the control electrode 25, the more positive the potential of this electrode the smaller the value of this internal impedance, and conversely the more negative the potential of this electrTople 1e value of the potential of the control electrode 25 with respect to cathode 20 is determined by the value of the source of voltage 26 and the IR- drop in resistance 19.

H, with such a circuit arrangement, an increase in the voltage of source 13 should take place, thisvwould tend to increase the current through the regulator 22 and resista-nce 19. However, an increase in the current through resistance 19 will increase the drop of potential across its terminals, thereby making the potential of the control electrode 25 more negative. This change in the potential of the control electrode 25 will increase the internal impedance of tube 22 a much more than proportional amount, thereby restricting the rise in current to a small value so that the space current of amplifier 2 is maintained substantially constant in spite of the increase in the voltage of source 13. In a similar manner if the voltage of source 13 should decrease in value, the drop in potential across the terminals of resistance 19 would likewise decrease so as to make more positive the potential of the control electrode 25, thereby decreasing a much' more than proportional amount the internal impedance of tube 22 and restrictin the decrease in current to a small value. 11 order that the potential of control electrode 25 may produce either adecreasc or an increase in the current through tube 22 as above described, tube 22 must necessarily operate normally below its saturation current. Thus it is seen that the vacuum tube regulator 22 serves to hold substantially constant the current supplied to amplifier 2.

The vacuum tube regulator 22 will also prevent the incoming signals impressed on the input circuit of tube 2- from producing a substantial change in the space current of tube 2, since any change in the space current between cathode 4 and anode 6 of tube 2 will produce a corresponding change in the current flowing through resistance 19. Since resistance 19 and vacuum tube regulator 22 are also common to the input circuit of amplifier 3, it follows, therefore, that the signal variations impressed on the input electrodes of tube 3, will be in the form of changes of voltage only. This arrangement also enables practically all of the amplified voltage from the amplifier 2 to be impressed on the input terminals of the succeeding amplifier, owing to the fact that none of the amplified ,yoltage will be wasted by passing through the resistance 19 and regulator 22.

While the vacuum tube regulator of this invention is shown in the drawing to be applied only to the first stage of an amplifier set, it is apparent that it may be applied to as many stages of an amplifier set as is desired. However, its use in the first stage or first few stages of an amplifier set is more important since any variation in the output voltage of these stages will be amplified along' with the signal variations by the succeeding stages so as to produce a serious distortion in the amplified-signals impressed on the receiving apparatus. vacuum tube regulator may be of any suitable type containing a cathode, an anode and Although the a control electrode, it,has been found that the regulator will work more efliciently if it is of the same general'type as the amplifier with which it is associated. The value of the resistance which is connected between the control electrode and the cathode of the regulator may be varied within wide limits but it is preferablethat it be of a value considerably larger than the output circuit impedance of the amplifier to which it is connected. While the source of voltage 26 for the control electrode of regulator 22 may be varied considerably in value, it has been found preferable to give this source of voltage such a value as to make the internal -impedance of the regulator 22 suificient when takenin connection with resistance 19 that only approximately one-third of the voltage of. source 13 is applied between the anode and cathode of the amplifier 2.

It is to be understood that this invention is .not limited to the s ecific embodiment above described but that 1t may be embodied in many and widely different forms without departing from this invention as defined in the appended claims. It is also to be understood that the phrase vacuum tube as used in this specification and the appended claims is intended also to cover gas filled tubes; and that the phrase vacuum tube repeaters is not limited to vacuum tube amplifiers.

What is claimed is:

,1. In an electric system, a vacuum tube having an input and output circuit, a source of current for said output circuit, means for supplying impulses to said input circuit,

and means comprising a second vacuum tube i for maintaining the current in said output v having an input and an output circuit, a'isa source of voltage for said output circuit, a source of signals for said input circuit, means for preventing said signals or variw tions in said source from producing a substantial change in the current of a portion of said output circuit, said means comprising a second vacuum tube having electrodes in said portion, and means responsive to a change in the current in said portion for producing a change in the electrical condition of one of said electrodes whereby a greater change tends to take place in the current through said second tube.

3. In an electric system, a vacuum tube having an input and an output circuit, a source of signals for said input circuit, a source of current for said output circuit, a second vacuum tube having an anode, a cathode and a control electrode, said anode and cathode being connected in said output circuit, and means for controlling the potential of said control electrode to prevent the output current of said first tube from changing regardless of said signals or variations in said source of current.

4. In an electric system, a vacuum tube having an input circuit and an output circuit, a source of current for said output circuit, a source of signals for said input circuit, and means for rendering the value of the current in said output circuit independent of said signals, said means comprising a second vacuum tube having an anode, a cathode and a control electrode, said cathode and anode being connected in said output circuit, and an impedance connected between said cathode and said control electrode and common to said output circuit.

5. In an electric system, a vacuum tube having an input circuit and an output circuit, a source of current for said output circuit, means for impressing signals on said input circuit. and means for rendering the current of said output circuit independent of said signals or fluctuations in said source, said second means comprising a vacuum tube in said output circuit. and means for varying the effective impedance of said second tube when said current tends to change.

6. In a multistage amplifier set, a plurality of vacuum tube amplifiers each having an input circuit and an output circuit, a source of electrical variations to be amplified by said amplifiers, and means comprising a Vacuum tube regulator common to the output circuit of one of said tubes and the input circuit of another of said tubes for causing said first mentioned amplifier to impress on said second mentioned amplifier, amplified variations from said source substantially in the form of changes of voltage only, said regulator being of such a character that in the normal operation of the set,

the regulator operates with a current substantially below its saturation current.

7. In a multi-stage amplifier set, a plurality of vacuum tube amplifiers connected in tandem, said amplifiers havinginput circuitS and output circuits, means for supplying current to said output circuits, at source of electrical variations, means for impressing said variations upon one of said tubes, and means for impressing upon a second amplefier of said set the amplified signals in the output circuit of said first amplifier substantially in the form of changes of voltage only, said second means comprising a third vacuum tube connected in the output circuit of said first amplifier, and means for varying the impedence of said third vacuum tube in response to a variation in the output circuit current whereby said change is reduced to a small value.

8. In a multi-stage amplifier set, a plurality of vacuum tube amplifiers connected in tandem, said amplifiers having input and output circuits, means for supplying current to said output circuits, :1 source of signals. means for impressing said signals upon one of said tubes and means for impressing upon a second vacuum tube of said vset. the amplified signals in the output circuit of said first amplifier substantially in the form of changes of voltage only, said third means comprising a third vacuum tube connected in the output circuit of said first tube, and means for varying the effective impedance of said third tube to counter-balance the tendency of said signals to change the output current of said amplifier.

9. In, a multi-stage amplifier set. a plir rality of vacuum tube amplifiers connected in tandem, said amplifiers having input circuits and output circuits, means for supplying current to said output circuits. at source of electrical variations, means tor impress ing said variations upon one of said amplifiers, and means for impressing upon a second amplifier of said set the amplified signals in the output circuit of said first amplifier substantially in the form of changes of voltage only, said third means comprising a third vacuum tube having an anode. a cathode and a control electrode. said anode and cathode being connected in the output circuit of said first amplifier, a resistance hetwcen said cathode and said control electrod and common to the output circuit of said first tube whereby changes in the output current of said first tube will produce changes in the potential of said control electrode.

10. In a multi-stagc amplifier set, a plurality of amplifiers. each having an input circuit and an output circuit, means for supi plying said output circuits with current. a resistance, a vacuum tube having a cathode. an anode and a control electrode, an output Hit! ltlf) llU alt

circuit for one of said amplifiers containing said resistance, and the cathode and anode of said tube, and a connection between said control electrode and said resistance. 7

'11. In an electric system, a vacuumtube having an input circuit and an output circuit, a source of current for said output circuit, means for impressing signals on said input circuit, and means for rendering the current of said output circuit substantially independent of said signals or fluctuations in said source, said means comprising a vacuum tube, the electrical characteristics of which are substantially the same as said first tube, and means for var ing the effective impedance of said secon tube when said current tends to change. I

12., In an electric system, a vacuum tube having input and output electrodes, an input circuit and an output circuit, a source of current for said output circuit, a source of signals for said input circuit, and means for rendering the value of the current in said output circuit independent of said signals, said means comprising a second vacuum tube having an anode, a cathode, and a control electrode, said cathode and anode being connected in said output circuit, and a re sistance connected between said cathode and said control electrode, and common to said output circuit, said resistance having a value at least as large as the effective impedance between the output electrodes of said first tube.

13. In a repeating system, a vacuum tube having input and output circuits and having a cathode and an anode in said output circuit, a source of voltage in said output circuit, means to impress impulses on said input. circuit, means in said output circuit to receivethe repeated impulses, an impedance in said output circuit between said source and said anode and arranged in shunt to said receiving means, and means responsive to changes in said source forchanging the value of said impedance.

eoauee its saturation current.

15. In an electric system, a repeater having an input circuit and an output circuit, a

source of voltage for said outpiitcircuit,

means for supplying impulses to be repeated to said input circuit, and means for maintaining substantially constant a characteristic of a portion of said output circuit, said means comprising a vacuum tube, and means I responsiveto a change in a characteristic of 1a. In an electric system, a vacuum tube having an input 'circuit' and an output cir cuit, a source of voltage for said output circuit, means for supplying impulses to said said portion for varying the-impedance of said tube whereby said change is reduced to a small value. 1

16. In an electric system, a vacuum tube normally operates with a space current below having input terminals and output terminals, a source of voltage for said output terminals, means for supplying impulses to saidv input terminals, a receiving device, connectIOIIS bBtWGGH said output terminals .and sa1d receiving devlce, a shunt path to sa1d connections containing a second vacuum tube,

and means responsive to a change in an electrical characteristic of said pathfor con-. trolling said second tube whereby said change is reduced to a small value.

17. In an electric system, a vacuum tube having an input circult and a branched out put circuit, a source of space current for said tube, an outgoing line associated with one branch of said output circuit, means for supplying impulses tosaid input circuit, and means located in a second branch of said output circuit and comprising a second vacuum tube for causing the space current of said first tube to be substantially independent of small variations in the voltage of said source, said source being of such a value that said second tube normally operates with a space current below its saturation current.

HARRY READ.

ssi 

